Tyrosine hydroxylase is the rate-limiting enzyme in the catecholamine biosynthetic pathway of animals. The catecholamine family of hormones and neurotransmitters includes dopamine, adrenaline and noradrenaline. Human pathologies including Parkinson's disease, schizophrenia and heart disease have been linked to catecholamine levels. Tyrosine hydroxylase is a promising drug target for these diseases, but no structural information is currently available to assist in drug development.